Log Message:
libopenmpt: update to 0.5.7.

### libopenmpt 0.5.7 (2021-03-20)

 *  [**Sec**] Possible null-pointer dereference read caused by a sequence of
    `openmpt::module::read`, `openmpt::module::set_position_seconds` with a
    position past the song end, and another `openmpt::module::read` call.
    (r14363)

 *  IT: Instrument / sample panning was reset on note-off / fade commands.
 *  IMF: Set Finetune is now implemented correctly.
 *  Fixed excessive memory consumption with malformed files in various formats.